Electronic Supplementary Materials Differential effects of prone position in COVID-19-related ARDS in low and high recruiters

Electronic Supplementary Materials

Differential effects of prone position in COVID-19-related ARDS in low and high recruiters

Supplementary Methods

Measurements was performed during volume control with Evita XL or Infinity C500 ventilators (Dräger Medical, Lübeck, Germany) in either supine semi-recumbent (30°) position or in prone mild reverse Tredelenburg (15°) position. Chest CT images done as part of daily management were also analyzed.

Partial pressure of oxygen/ inspired fraction of oxygen (PaO

/FiO

) and ventilatory ratios were assessed at clinical positive end-expiratory level (PEEP). At each timepoint, airway opening pressure (AOP) and recruitment-to-inflation ratio (R/I) were determined, as previously described [4, 5]. Briefly, the R/I ratio was determined with high PEEP set at 15 cmH

O (for 30 minutes) and low PEEP set at 5 cmH

O. AOP was assessed during a low flow insufflation (<7 l/min), as previously described [4]. The recruited volume (Vrec) from low to high PEEP (i.e. 5 to 15 cmH

O) divided by the effective pressure change gave the compliance of the recruited lung (Crec); the ratio of Crec to the respiratory system compliance (Crs) at PEEP 5 cmH

O led to the R/I. In the event that AOP was >5 cmH

O (i.e. low PEEP), R/I was calculated with AOP instead of 5 cmH

O [4, 5]. During R/I ratio measurement, oxygenation was estimated using the pulse oximetry saturation/inspired fraction of oxygen ratio (SpO

/FiO

).

Data are expressed as median (first-to-third quartile) or count (%). Comparisons were done using Mann-Whitney U or Fisher’s exact test. Correlations were assessed with the Rho Spearman’s correlation test. Differences between groups across timepoints were tested by one-way ANOVA for repeated measures or Friedman test, as appropriate.

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Supplementary Table S1 - Patients characteristics and respiratory mechanics at baseline All patients

(n=18)

Low recruiters (n=9)

High recruiters (n=9)

P

Demographics

Age – years 63 [59-69] 63 [61-71] 60 [58-67] 0.423

Male gender – n (%) 11 (61) 5 (56) 6 (67) >0.99

Body mass index – kg/m² 31 [27-33] 29 [24-36] 33 [29-33] 0.421

Simplified acute physiology score II 38 [31-44] 39 [34-45] 33 [30-45] 0.681

Delays – Days

Between symptoms and ICU admission 9 [7-9] 9 [7-11] 9 [8-9] 0.886

Between ICU admission and intubation 1 [0-4] 1 [0-4] 3 [2-7] 0.234

Between intubation and inclusion 2 [0-4] 3 [1-10] 1 [1-2] 0.097

Consolidation on CT scan – n (%) 9 (50) 6 (67) 3 (33) 0.350

High flow oxygen therapy > 24 hours – n (%) 12 (67) 4 (44) 8 (89) 0.130

Lowest PaO2/FiO2 before inclusion – mmHg 77 [58-104] 90 [65-109] 68 [49-100] 0.297

Number of prone cycling at inclusion 1 [0-2] 1 [0-2] 1 [0-2] 0.646

Baseline respiratory data (supine position)

Tidal volume– mL/kg(PBW) 5.7 [5.3-6.1] 5.6 [5.3-6.0] 5.9 [5.3-6.1] 0.746

Respiratory rate 20 [18-24] 20 [18-25] 21 [19-24] 0.382

PEEP – cmH2O 11 [9-14] 12 [9-13] 10 [10-15] 0.883

FiO2 – % 60 [45-80] 50 [50-90] 60 [53-78] 0.968

Airway opening pressure > 5 cmH2O – n (%) 4 (22) 1 (11) 3 (33) 0.580

Peak pressure – cmH2O 36 [29-40] 34 [31-39] 37 [29-41] 0.985

Plateau pressure – cmH2O 24 [20-25] 23 [21-27] 24 [20-25] 0.678

Driving pressure – cmH2O 11 [9-15] 12 [10-14] 10 [10-13] 0.477

Crs – ml/cmH2O 32 [25-42] 26 [25-37] 41 [26-45] 0.267

Volume of the recruited lung – ml 236 [131-338] 133 [113-198] 330 [261-448] <0.001 Compliance of the recruited lung – ml/cmH2O 24 [13-36] 13 [11-20] 36 [26-50] <0.001

SpO2/FiO2a 1 [-1.5 to 9] 1 [-1.5 to 9] 28 [3-38] 0.042

PaO2/FiO2 ratio – mmHg 127 [99-153] 128 [98-153] 127 [100-154] 0.982

PaCO2 – mmHg 44 [36-52] 48 [41-52] 40 [35-51] 0.372

Ventilatory ratio 1.29 [1.21-1.74] 1.33 [1.12-2.12] 1.26 [1.22-1.69] 0.779

Discharged alive from ICU 15 (83) 6 (67) 9 (100) 0.210

Data are expressed as median [first to third quartile] or counts (percentage). PBW: predicted body weight; P EEP: positive end-expiratory pressure; ICU: intensive care unit; FiO2 : inspired fraction of oxygen; SpO2 : pulse oximetry saturation; Crs: compliance of the respiratory system.

aSpO2/FiO2 = SpO2/FiO2at PEEP 15 cmH2O - SpO2/FiO2at PEEP 15 cmH2O.

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